Conventional detergent comprising surfactant as an essential ingredient contains a builder as an auxiliary component to the surfactant to thereby improve its detergency. As the builder, known are inorganic compounds which are alkaline in water, and polymers of unsaturated aliphatic carboxylic acids. As examples of the former, mentioned are sodium and potassium carbonates, hydrogencarbonates, phosphates, polyphosphates and silicates, as well as zeolite, etc.; while examples of the latter include polyacrylic acid, polymaleic acid, polyitaconic acid, etc.
Of those builders, much used are phosphates, polyphosphates and zeolite, as they are effective, economical and easy to handle. However, these are problematic from the viewpoint of the protection of the global environment in that phosphates and polyphosphates eutrophicate lakes, marshes and rivers while zeolite precipitates in rivers, etc.
Accordingly, it is desired to develop some other builders, of which the capability, especially, the chelating ability (calcium ion-sequestering ability) is good like that of conventional builders, which are well biodegradable to be gentle to the environment, without remaining for a long period of time on the earth, and are therefore not problematic from the important viewpoint of the protection of the global environment, and which are economical.
Given that situation, Japanese Patent Laid-Open No. 239127/1993 discloses chelatable and biodegradable, crosslinked polymers suitable for builders. To prepare the polymers, water-soluble oligomers, which have little chelatability by themselves but contain biodegradable low-molecular components, are crosslinked at their main chains with a crosslinking agent, such as polyethylene glycol, citric acid, tartaric acid or the like, via a biodegradable ester or amido group to thereby increase their molecular weight, and the resulting crosslinked polymers are modified to have chelatability. However, though having a low molecular weight thereby to have increased biodegradability, the linear polyacrylic acid moiety in those crosslinked polymers is hardly biodegradable, and, in addition, the polymers contain hardly-biodegradable high-molecular-weight linear polyacrylic acids to no small extent. Therefore, the biodegradability of the crosslinked polymers disclosed is not satisfactory. Another problem with the polymers is that the method for producing them is not simple, as requiring two steps, one for polymerizing the oligomer and the other for crosslinking the polymerized oligomer, and requiring the special crosslinking agent.
Japanese Patent Laid-Open No. 80377/1975 discloses acrylic acid or acrolein polymers and their modified derivatives or copolymers usable as builders. However, these are all problematic in that their chelatability and biodegradability are not satisfactory.
Accordingly, it is desired to develop polymers having good chelatability and good biodegradability and therefore suitable to builders and to develop methods for efficiently producing them.
In the field of dispersants for inorganic pigments, sodium polyacrylate or the like is used for lowering the viscosity of slurry dispersions and for improving the viscosity stability thereof. However, polyacrylic acid is not biodegradable. Also in this field, therefore, it is desired to develop some other dispersants which are biodegradable without remaining on the earth for a long period of time and which are economical.
The present invention is to provide an unsaturated carboxylic acid polymer having good chelatability and good biodegradability and therefore suitable to builders, to provide a method for efficiently producing it, and to provide a builder for detergent, a detergent composition and a dispersant containing the polymer as the constituent ingredient.